The invention relates to a tomographic apparatus for producing transverse layer images of a radiographic subject with a radiation measuring arrangement comprising a radiation source which produces a fan-shaped radiation beam penetrating the radiographic subject, the extent of which beam in the layer plane is of such dimensions that the entire radiographic subject is penetrated, and also comprising a radiation receiver which determines the intensity of radiation behind the subject by scanning the projected radiation beam, and having also a driving mechanism for the measuring arrangement to effect rotational movements of the radiation measuring arrangement, and a measured value converter to transform the signals supplied by the radiation receiver into a layer image wherein the radiation receiver consists of a row of detectors, the detectors of which being connected by one pole to a common voltage supply device and the number of detectors being selected according to the desired image resolution.
It is known to use as detectors xenon-detectors lying at high voltage in the measured value converter as ionization chambers. Thus, all the image elements of the angular position, per angular position of the measuring arrangement, are measured simultaneously by way of a corresponding number of individual X-ray detectors, and the signals of the detectors are subsequently processed in parallel in separate measuring channels. Various types of errors occur with such a measuring arrangement. One cause of error resides in the differing sensitivities of the X-ray detectors due to their manufacturing tolerances. These errors do not change in the course of the operation. It is therefore sufficient to detect these errors once. There are, however, other errors which vary in the course of time, i.e., the differences in amplification of the measuring channels coordinated to the individual detectors of the measured value converter. These differences in amplification emanate, on the one hand, from structural element tolerances, but also, on the other hand, from external influences, e.g., temperature and aging influences.